Does a Prius really need time to "warm up"?

Don't assume from this that you get better mileage by warming up the engine before driving. Generally it's better to get in and drive, just try to take it easy for the first minute or so.

A cold engine produces worse mileage for all cars. It's not limited to the Prius.

Tom

 

The warming up process is for emissions output efficiency. I usually let it warm up because your getting crappy gas mileage either way. Just something you have to deal with, thats why short trips kill the mileage.

 

All cars need to warm up. Prius does it faster than any other car by reusing the heat from the exhaust.

 

Short answer: Yes, especially in cold temperatures. As with any car, a cold engine is inefficient.

As efusco said, to confirm this, simply take a look at the histogram screen, shown in minutes (hold the DISP steering wheel button to switch between the 5 min/1 min views). In my L/100km view (outside US), the first column is simply pathetic, way over the 10 L/100km limit of the display (way lower than 23 US MPG). The second minute gets better, and so on. The colder the outside temp, the longer it will take until the columns get into average gas consumption numbers for the car.


If you have a hypermiller fiber, you may want to learn about the Prius stages. In the first 45-50 seconds (stage 1a), the ICE is warmed up in a way by which it cannot produce sufficient force to drive the car; the motor/traction battery is then used to do so (unless you go pass the ECO zone of the HSI into the PWR zone: the ICE will then provide power, in an inefficient manner).

• During that first 45 s. (probably longer in the winter months, depending on where you live: haven’t tested this last winter), you should let the car parked or drive with very mild acceleration, to avoid draining the traction battery (which need to be charged back, using gas, after the engine has warmed up).
• I’ve started using this method (waiting 45 s., parked) in the last weeks and have seen a 0.2 L/100km reduction for my short commute.
• Note that without a ScanGauge or such, it is not easy to know when you have left stage 1a (coolant temp >40°C), which is long before the engine stops by itself (coolant temp >70°C). Therefore, waiting for the ICE to turn off by itself before moving the car wouldn't be smart at all. I found that by listening to the ICE rpm while moving can help: if it is constant, even when your acceleration rate varies (gas pedal), you are still in stage 1a and the motor & battery are moving you while the ICE warms up at a constant rpm; if its speed is changing, you are out of stage 1a. By trial and error, you should find out how long you should wait to get out of stage 1a to get optimum fuel economy.
• If you don't want to bother with this, simply avoid brisk accelerations for the first 1-2 minutes.

Also, when doing errands, plan your first leg to be the longest.

In the winter, the phenomenon will be more important and the warming up times will be longer. A block heater will help. The stats I begun to accumulate last winter indicate that a block heater used for 3.5h in freezing temps will reduce gas consumption by about 0.4-0.6 L/100Km. Depending on your electricity rate, the cost should be minimal (amount of money saved on gas may or may not be more than the associated electricity bill).

I hope this answers your question.

 

You can generate some hard data yourself by:
(1) Resetting a Trip gauge at startup, and watch MPG as the engine warms, possibly resetting the gauge multiple times during warmup;
(2) Getting a ScanGauge or other engine monitor, and watching current MPG during warmup;
(3) with above engine monitor, watch GPH (gallons per hour) during warmup, including during stationary idling. I posted some numbers many moons ago.

 

Auto Enginuity has a utility called "Speed Tracer" which claims to calculate the vehicle MPG. This is not a calibrated utility and this is only the second time I've run it. However, I had to get some groceries at 3:00 AM and here are the results:

Obviously, I missed replicating the red light stop on the return trip. Also, it looks like low speeds, the MPG doesn't quite look right. I may not have gone into Stage 4 before arriving at Krogers. This would make a major impact in the MPG. But having data, even flawed data, is better than none as long as we realize this was an informal test. A better protocol might give a better result. NOTE: the Speed Tracer has not been throughly tested and these numbers, especially the coast down numbers, are VERY SUSPECT!

ROUTE:
[ame="http://maps.google.com/maps?f=d&source=s_d&saddr=2009+Drake+Avenue,+Southwest,+Huntsville+AL&daddr=9011+Randall+Rd+SW,+Huntsville,+AL+35802&geocode=FdiPEQIdl8LW-imBmcXFt2xiiDFs7rsn3ceeqA%3BFeTCEAIdFAbX-ilfG8a_sBJiiDHu2IUHDRAYlg&hl=en&mra=ls&sll=34.7266,-86.639248&sspn=0.259032,0.470352&ie=UTF8&z=13"]2009 Drake Ave SW, Huntsville, AL 35801 to 9011 Randall Rd SW, Huntsville, AL 35802 - Google Maps[/ame]

Bob Wilson

 

What is the speed profile of your first 5 minute drive? I have never seen anything over 40 MPG during the first 5 minutes even with the block heater and best weather and road conditions. Thanks!

 

the answer to that probably lies in the terrain profile... which my guess is all downhill.